| The most important characteristics of soils is its charges on the surface. Because of its huge quantity of electric charges, its wide distribution and relatively long distance force action, the physical, chemical and biochemical processes concerned with ion, proton and electron exchanging and handing around should be deeply affected, the electro-chemistry has being the front of soil science since 3 decades before. The charge properties, the interaction between the surface and the ions, electron and protons are the focus of the study in soil electro-chemistry.The Theory of Double Layer is the basic theory of soil surface charge. In order to gain the number of potential and charge density in any place of the double layer, the formula of Gouy-Chapman should be used. But when using this formula to calculate those indexes, the surface potential and the surface charge density are needed. However, there is no satisfactory method to measure them. Li Hang presented a new method to measure the surface potential and the surface charge density. This method can get surface potential and surface charge density without the data of SSA and makes it more easy to measure the surface charge properties.The method has been used in this experimental study. Neutral purple soil, acid purple soil and calcareous purple soil were taken as the experimental materials. The charge quantity, the surface potential, the surface charge density, the surface electric field strength and SSA was measured. The experimental result has compared with the result measured by traditional method. The effect of electrolyte concentration, temperature, accompanying anion type, electrolyte type and pH on the surface charge properties was studied, too. The interaction between the surface and the heavy mental ions was also conducted. The experimental result as follows:Firstly, the surface potential of the acid purple soil, neutral purple soil and calcareous purple soil is -0.16- -0.18 V, -0.17- -0.19 V , -0.18- -0.19 V respectively; the surface charge density is -0.26--0.44 C m-2, -0.37- -0.59 C m-2, -0.58- -0.67 C m-2; the electric field strength is more than 108 J m-1 C-1; and the SSA is 26, 45. 41m2 g-1. The experimental result is higher than the one gained by the traditional method. The result of surface potential in 2:1 electrolyte type is lower than the one in 1:1 type, and the former is about 50% of the latter; but the charge quantity, surface charge density is almost same in both type.Secondly, with the increasing of electrolyte concentration, the charge quantity and the surface charge density increase a little; but the surface potential decreases. The up-limited surface charge density of acid, neutral and calcareous purple soils is -0.19 C m-2, -0.48 C m-2, -0.64 C m-2, and the down-limited surface charge density is -0.26 C m-2, -0.60 C m-2, -0.70 C m-2 .respectively. It can be speculated that the permanent charge accounts for 70%~90% of the total charge quantity; therefore, the permanent charge is the main type of the soil samples. The result is identical with the main mine in the soil samples. And the result is identical with the result gained by the method of Mehlich.Thirdly, the effect of accompanying anion on the surface charge is little. The effect of pH on the surface charge properties is not obvious. When pH < 5, the surface potential decreased about 0.1V, but the surface charge density increased a little; when pH > 5, there is no changed about the potential and the surface charge density. Those results ascribe to the fact that permanent charge is the main type of the soil sample. With the raise of temperature, the surface charge quantity, surface potential, surface charge density decrease sharply. For example, when the temperature changed from 298K to 313K, the charge quantity decreased about a half, the surface potential decreased 20 percent, and the surface charge density deceased 30 percent.Fourthly, the effect of pH and the ion strength on the adsorption of heavy mental ions (Pb2+, Cu2+) showed that there are static ad... |
